#include <iostream>
#include <string>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unordered_map>
#include <sys/stat.h>
#include <fcntl.h>

#define COMMAND_SIZE 1024
#define FORMAT "[%s@%s %s]# "

//下面是shell定义的全局数据

//1.命令行参数表
#define MAXARGC 128
char* g_argv[MAXARGC];
int g_argc = 0;

//2.环境变量表
#define MAX_ENVS 100
char* g_env[MAX_ENVS];
int g_envs = 0;

//3.别名映射表
std::unordered_map<std::string, std::string> alias_list;

//关于重定向，我们关系的内容
#define NONE_REDIR 0
#define INPUT_REDIR 1
#define OUTPUT_REDIR 2
#define APPEND_REDIR 3
int redir = NONE_REDIR;
std::string filename;

//for pwd
char cwd[1024];
char cwdenv[1024];

//退出码
int lastcode = 0;

//获取环境变量中的用户名
const char* GetUserName()
{
    const char* name = getenv("USER");
    return name == NULL ? "None" : name;
}

//获取环境变量中的主机名
const char* GetHostName()
{
    const char* hostname = getenv("HOSTNAME");
    return hostname == NULL ? "None" : hostname;
}

//获取环境变量中的当前路径
const char* GetPwd()
{
    //const char* pwd = getenv("PWD");
    const char* pwd = getcwd(cwd, sizeof(cwd));
    if(pwd != NULL)
    {
        snprintf(cwdenv, sizeof(cwdenv), "PWD=%s", cwd);
        putenv(cwdenv);
    }
    return pwd == NULL ? "None" : pwd;
}

//获取环境变量中的当前用户家目录
const char* GetHome()
{
    const char* home = getenv("HOME");
    return home == NULL ? "" : home;
}

//初始化环境变量表
void InitEnv()
{
    extern char** environ;
    memset(g_env, 0, sizeof(g_env));
    g_envs = 0;

    //拷贝全局环境变量environ
    for(int i=0; environ[i]; ++i)
    {
        g_env[i] = (char*)malloc(strlen(environ[i])+1);
        strcpy(g_env[i], environ[i]);
        ++g_envs;
    }
    g_env[g_envs++] = (char*)"TXP=txp txp";
    g_env[g_envs] = NULL;

    //复制到当前环境变量env中
    for(int i=0; g_env[i]; ++i)
    {
        putenv(g_env[i]);
    }

    environ = g_env;
}

//清理环境变量表
void clean()
{
    for(int i=0; g_env[i]; ++i)
    {
        free(g_env[i]);
        g_env[i]=NULL;
    }
    g_envs = 0;
}

//command
bool Cd()
{
    if(g_argc == 1)//单独一个cd时
    {
        std::string home = GetHome();
        if(home.empty()) return true;
        chdir(home.c_str());
    }
    else //cd + 路径时
    {
        std::string where = g_argv[1];
        if(where == "-");
        else if(where == "~");
        else 
        {
            chdir(where.c_str());
        }
    }
    return true;
}

bool Echo()
{
    if(g_argc == 2)
    {
        std::string opt = g_argv[1];
        if(opt == "$?")
        {
            std::cout<<lastcode<<std::endl;
            lastcode = 0;
            return true;
        }
        if(opt[0] == '$')
        {
            std::string env_name = opt.substr(1);
            const char* env_value = getenv(env_name.c_str());
            if(env_value)
                std::cout<<env_value<<std::endl;
            return true;
        }
    }
    return false;
}

//简化路径
std::string DirName(const char* pwd)
{
#define SLASH "/"
    std::string dir = pwd;
    if(dir == SLASH) return SLASH;
    auto pos = dir.rfind(SLASH);
    if(pos == std::string::npos) return "BUG?";
    return dir.substr(pos+1);
}

//制作命令行提示符
void MakeCommandLine(char cmd_prompt[], int size)
{
    snprintf(cmd_prompt, size, FORMAT, GetUserName(), GetHostName(), DirName(GetPwd()).c_str());
    //snprintf(cmd_prompt, size, FORMAT, GetUserName(), GetHostName(), GetPwd());
}

//打印命令行提示符
void PrintCommandPrompt()
{
    char prompt[COMMAND_SIZE];
    MakeCommandLine(prompt, sizeof(prompt));
    printf("%s", prompt);
    fflush(stdout);
}

//获取用户输入的命令
bool GetCommandLine(char*out, int size)
{
    char *c = fgets(out, size, stdin);
    if(c == NULL) return false;
    out[strlen(out)-1] = 0; //清理\n
    if(strlen(out)==0)  return false;
    return true;
}

void TrimSpace(char* cmd, int& end)
{
    while(isspace(cmd[end])) ++end;
}

//重定向分析
void RedirCheck(char* cmd)
{
    redir = NONE_REDIR;
    filename.clear();
    int start = 0;
    int end = strlen(cmd)-1;

    //"ls -l > file.txt" -> "ls -l" "file.txt"
    while(end > start)
    {
        if(cmd[end] == '<')
        {
            cmd[end++] = 0;
            TrimSpace(cmd, end);
            redir = INPUT_REDIR;
            filename = cmd+end;
            break;
        }
        else if(cmd[end] == '>')
        {
            if(cmd[end-1] == '>')
            {
                //>>
                cmd[end-1] = 0;
                redir = APPEND_REDIR;
            }
            else
            {
                //>
                redir = OUTPUT_REDIR;
            }
            cmd[end++] = 0;
            TrimSpace(cmd, end);
            filename = cmd+end;
            break;
        }
        else 
        {
            --end;
        }
    }
}


//分析用户输入的命令
bool  CommandParse(char* commandline)
{
#define SEP " "
    g_argc = 0;
    g_argv[g_argc++] = strtok(commandline, SEP);
    while((bool)(g_argv[g_argc++] = strtok(nullptr, SEP)));
    --g_argc;
    return g_argc > 0 ? true : false;
}

//测试
void PrintArgv()
{
    for(int i=0; g_argv[i]; ++i)
    {
        printf("g_argv[%d]->%s\n", i, g_argv[i]);
    }
    printf("g_argc=%d\n", g_argc);
}

//检测并执行内建命令
bool CheckAndExecbuiltin()
{
    std::string cmd = g_argv[0];
    if(cmd == "cd")
    {
        return Cd();
    }
    else if(cmd == "echo")
    {
        return Echo();
    }
    else if(cmd == "export")
    {
        ;
    }
    else if(cmd == "alias")
    {
        ;
    }
    
    return false;
}

//执行命令
int Execute()
{
    pid_t id = fork();
    if(id == 0)
    {
        //child
        //子进程检测重定向情况
        int fd = -1;
        if(redir == INPUT_REDIR)
        {
            fd = open(filename.c_str(), O_RDONLY); 
            if(fd<0) exit(1);
            dup2(fd, 0);
            close(fd);
        }
        else if(redir == OUTPUT_REDIR)
        {
            fd = open(filename.c_str(), O_CREAT | O_WRONLY | O_TRUNC, 0666);
            if(fd<0) exit(2);
            dup2(fd, 1);
            close(fd);
        }
        else if(redir == APPEND_REDIR)
        {
            fd = open(filename.c_str(), O_CREAT | O_WRONLY | O_APPEND, 0666);
            if(fd<0) exit(2);
            dup2(fd, 1);
            close(fd);
        }
        else 
        {}
        //程序替换
        execvp(g_argv[0], g_argv); 
        exit(1);
    }
    //father
    int status;
    pid_t rid = waitpid(id, &status, 0);
    if(rid > 0)
    {
        lastcode = WEXITSTATUS(status);
    }

    return 0;
}

int main()
{
    //模拟启动时获取环境变量表
    InitEnv();

    while(true)
    {
         //1.输出命令提示符
        PrintCommandPrompt();
        
        //2.获取用户输入的命令
        char commandline[COMMAND_SIZE];
        if(!GetCommandLine(commandline, sizeof(commandline))) continue;

        //3.重定向分析
        RedirCheck(commandline);
        
        //测试
        //printf("redir:%d, filename:%s\n", redir, filename.c_str());

        //4.命令行分析
        if(!CommandParse(commandline)) continue;
        //PrintArgv();
        
        //5.检查并处理内建命令
        if(CheckAndExecbuiltin()) continue;

        //6.执行命令
        Execute();
    }

    //清理环境变量表
    clean();

    return 0;
}
